The present invention relates to a freshness retaining agent to be placed in a refrigerator or a food storage cabinet for preventing decrease in the freshness of meat, fish, vegetables, etc. for a long period of time.
In this field of art, active carbon powders pretreated to absorb ethylene are known to be useful for maintaining the freshness of vegetables and fruits in the refrigerator or the like. However, decreases in the freshness of vegetables and fruits occur even in the ethylene-lean environment and, moreover, a putrefactive process is also involved. Therefore, the use of active carbon lacking in biocidal activity is not effective enough to maintain the freshness of those easily perishable foods.
On the other hand, allyl isothiocyanate (CH.sub.2 .dbd.CHCH.sub.2 NCS), which is contained in Japanese horseradish (wasabi) and mustard, is known to inhibit growth of pathogenic microorganisms. In particular, this substance has antibacterial activity against Escherichia coli, Staphylococcus aureus, Proteus species and Vibrio parahaemolyticus. It is, therefore, effective as a freshness retainer for fish and meat. Allyl isothiocyanate prevents emanation of ethylene, which is known to be an aging hormone for vegetables and fruits, to thereby protect vegetables and fruits from aging. Therefore, it is also useful as a freshness retainer for those foodstuffs. Japanese horseradish extracts and mustard extracts, which contain allyl isothiocyanate as a chief component, have been approved as food additives and can be safely used in the refrigerator where foodstuffs are preserved. Furthermore, allyl isothiocyanate shows its freshness retaining action in gaseous phase contact and, therefore, produces a freshness retaining effect even at a low concentration of about 0.3 ppm.
Isothiocyanic acid compounds are liquids sparingly soluble in water and having high volatility. Therefore, in the art, attempts have been made to place a paper or mineral carrier impregnated with such a compound in the refrigerator for the purpose of retaining the freshness of foodstuffs. However, the active ingredient is evaporated off rapidly from the carrier, resulting in loss of the effect in one to two days. In view of the circumstances, the present inventors made intensive investigations to find a method for retaining the freshness of foods in the refrigerator or food storage box for a very long period of time. As a result, the inventors previously proposed a gel-form freshness retaining agent comprising an isothiocyanic acid compound and a specific component such as a natural polysaccharide or an isoparaffin (Japanese Kokai Tokkyo Koho H09-51787). This freshness retaining agent emits the active ingredient over about one month. In cases where a fairly long period of time is required for transportation, for example by ship, however, the performance of this agent is not satisfactory as yet. Furthermore, when it is placed in the household refrigerator, it is necessary to check the freshness retaining agent frequently for its effectiveness; this is troublesome. Accordingly, a freshness retaining agent with which the freshness retaining effect will be maintained persistently over a still longer time is desired.
A primary object of the present invention is to provide an excellent freshness retaining agent with which the freshness of meat, vegetables and fruits in a refrigerator or a food storage box over a very long period of time. The present inventors made intensive investigations to achieve the above object. As a result, they found that the above object can be accomplished by forming a gel composition from a Japanese horseradish extract, a mustard extract or an isothiocyanic acid compound such as allyl isothiocyanate, and a specific component or components. The present invention has now been developed on the basis of such findings.